As is well known, motorized garage door operators automatically open and close a garage door through a path that is defined by an upper limit and a lower limit. The lower limit is established by the floor upon which the garage door closes. The upper limit can be defined by the highest point the door will travel which can be limited by the operator, the counterbalance system, or the door track system's physical limits. The upper and lower limits are employed to prevent door damage resulting from the operator's attempt to move a door past its physical limits. Under normal operating conditions, the operator's limits may be set to match the door upper and lower physical limits. However, operator limits are normally set to a point less than the door's physical upper and lower limits.
Systems used to set operator limits are composed of switches used to terminate travel in the up and down directions. These mechanical switches are adjustable and can be used by the consumer or an installer to "fit" the door travel to a garage opening. These switches are mechanical and have a limited life span. Metal fatigue and corrosion are the most likely causes of switch failure. Another drawback of mechanical switches is that they can be wired in series with the motor which creates high current draw across the contacts of the switch causing the contacts to fail. A further limitation of limit switches is that the up and down limits, which must be set manually, can be improperly set or misadjusted.
Other limit systems employ pulse counters that set the upper and lower travel of the door by counting the revolutions of an operator's rotating component. These pulse counters are normally coupled to the shaft of the motor and provide a count to a microprocessor. The upper and lower limits are programmed into the microprocessor by the consumer or installer. As the door cycles, the pulse counter updates the count to the microprocessor. Once the proper count is reached, which corresponds to the count of the upper and lower limits programmed by the consumer or installer, the door stops. Unfortunately, pulse counters cannot accurately keep count. External factors such as power transients, electrical motor noise, and radio interference often disrupt the count allowing the door to over-travel or under-travel. The microprocessor may also lose count if power to the operator is lost or if the consumer manually moves the door while the power is off and the door is placed in a new position which does not match the original count.
Motorized garage door operators include internal entrapment protection systems designed to monitor door speed and applied force as the door travels in the opening and closing directions. During travel from the open to close and from close to open positions, the door maintains a relative constant speed. However, if the door encounters an obstacle during travel, the speed of the door slows down or stops depending upon the amount of negative force applied by the obstacle. Systems for detecting such a change in door speed and applied force are commonly referred to as "internal entrapment protection" systems. Once the internal entrapment protection is activated, the door may stop or stop and reverse direction.
Most residential operator systems are closed loop systems where the door is always driven by the operator in both the open to close to open directions. A closed loop system works well with the internal entrapment system wherein the operator is always connected to the door and exerting a force on the door when the door is in motion unless disconnected manually by the consumer. If an obstacle is encountered by the door, the direct connection to the operator allows for feedback to the internal entrapment device which signals the door to stop or stop and reverse. However, due to the inertia and speed of the door, and the tolerances in the door and track system, these internal entrapment systems are very slow to respond and some time passes after contacting an obstruction before the internal entrapment device is activated allowing the door to over-travel and exert very high forces on the object that is entrapped. Further, a closed loop operator system always has the capability of exerting a force greater that the weight of the door.
A method of internal entrapment protection on a closed loop system uses a pair of springs to balance a lever in a center position and a pair of switches to indicate that the lever is off-center signaling that an obstruction has been encountered. The lever is coupled to a drive belt or chain and balanced by a pair of springs adjusted to counterbalance the tension on the belt or chain so the lever stays centered. When an obstruction is encountered, the tension on the belt or chain overcomes the tension applied by the springs allowing the lever to shift off-center and contact a switch which generates an obstruction signal. Sensitivity of this system can be adjusted by applying more tension to the centering springs to force the lever to stay centered. This type of internal entrapment systems is slow to respond due to the inertia of the door, stretch in the drive belt or chain, and the components of the drive system.
Another method of the prior art on closed loop operator internal entrapment systems uses an adjustable clutch mechanism. The clutch is mounted on a drive component and allows slippage of the drive force to occur if an obstruction prevents the door from moving. The amount of slippage can be adjusted in the clutch so that a small amount of resistance to the movement of the door causes the clutch to slip. However, due to aging of the door system and environmental conditions that can change the force required to move the door, these systems are normally adjusted to the highest force condition anticipated by the installer or the consumer. Further, over time the clutch plates can corrode and freeze together preventing slippage if an obstruction is encountered. The drive systems on open loop operator systems are very efficient and can be back driven when the garage door is forced open as in a forced entry situation. Motor controls have been designed to use signals from the lower limit switch and the pulse counter to detect when this condition is occurring and start the motor to drive the door down again to its closed position. As mentioned before, the limit switches can fail and/or the pulse counter can miscount rendering this feature useless.
Another type of operator system is an open loop operator system wherein the door is not attached directly to the operator. In an open loop operator system when the door is moving from the closed to the open position, the door is lifted by the operator applying torque to the counterbalance system which reels in the cables attached to the door. When the door is moving from the open to closed position, the operator turns the counterbalance system to reel out the cables attached to the door and relies on gravity to move the door.
An open loop operator system has several advantages over a closed loop operator system. For example, the operator can never force the door to exert a downward force and any downward force can never be greater than the weight of the portion of the door that is in the vertical position. Further, vibrations from the operator and misalignments of the operator mountings will not affect movement of the door. The door and the operator are isolated from each other by the counterbalance system. Open loop operator systems are commonly used on vertical lift door systems where the door is always in the vertical position and has gravity exerting a downward force on the door at all times. However, open loop operators have not been successful in residential systems where the door is vertical when closed, but mostly horizontal when open. When the residential door is open, most of the weight of the door needed to affect the door's closing is carried by the horizontal track system. In an open loop operator system; however, when the door is beginning to close from the open position, there is only a small portion of the door in a vertical position. Therefore, only a small portion of the weight of the door is provided to initiate closing. In this condition, the door can bind or otherwise "hang up" and not continue to close. Further, if the door meets an obstruction during the motion from open to closed positions, only the weight of the portion of the door in the vertical position is applied to the obstruction. The gravity force creating the motion of the door in the open to closed direction is controlled by the counterbalance system wherein the cables that are attached to the bottom of the door are also attached to cable storage drums on the counterbalance system. As the operator turns the counterbalance system to peel off cables, gravity causes the door to move. This movement of the door and the counterbalance system causes the cable storage drums to turn, peeling off cable and at the same time cause winding of the springs inside the counterbalance system which store energy equal to the portion of the door that is in the vertical position. At anytime during normal movement of the door from open to close and close to open, the torsional energy stored in the counterbalance springs is about equal to the weight of the portion of the door in the vertical position. This close-to-balance condition between the door's weight in the vertical position and the energy stored in the counterbalance springs creates a condition in an open loop operator system that if there is a resistance to the movement of the door, the door will "hang up" and not move when the operator is peeling off cable. This "hang up" condition is where the door is not moving, but the operator is turning the counterbalance system and peeling off cable. This condition can be at any point of the door's travel from the open to the closed position, but is more prevalent when the door is open and beginning to close or if an obstruction is encountered during the closing cycle. If a "hang up" occurs and the cables are peeled off of the cable storage drums there is no longer a balanced condition between the energy stored in the counterbalance system and the weight of the door in the vertical position. When this unbalanced condition occurs, the cables become tangled around the cable storage drums requiring service before the door can be operated again or, worse, the door becomes dislodged and may come crashing down like a guillotine. This sudden movement of the door could cause injury or property damage. For these and other reasons, open loop operator systems have not been commercially successful due to the lack of motor controls needed to address these conditions.
Control of the cables on the cable storage drums is essential for open loop operator systems. Many methods have been employed such as mechanical cable snubbers and tensioners in an attempt to keep the cables from jumping off of the cable storage drums or becoming entangled. This control is made more difficult with lighter garage door panels or sections which have significantly reduced the weight of a garage door. Electrical means have also been employed to prevent the cables from jumping off of the cable storage drums or becoming entangled by means of pulse counters, cable tension switches, and current sensing devices. The mechanical snubbers or tensioners are not reliable due to wear and corrosion and the electrical methods fail for the same reasons mentioned above. In addition to using the aforementioned pulse counters to set the upper and lower limits of door travel, they may also be used to monitor the speed of the garage door to provide yet another method of internal entrapment. The optical encoders used for speed monitoring are normally coupled to the shaft of the motor. An interrupter wheel disrupts a path of light from a sender to a receiver. As the interrupter or chopper wheel rotates, the light path is reestablished. These light pulses are then sent to a microprocessor every time the beam is interrupted. Alternatively, magnetic flux sensors function the same except for the fact that the chopper wheel is made of a ferromagnetic material and the wheel is shaped much like a gear. When the gear teeth come in close proximity to the sensor, magnetic flux flows from the sender through a gear tooth and back to the receiver. As the wheel rotates, the air gap between the sensor and the wheel increases. Once this gap becomes fully opened, the magnetic flux does not flow to the receiver. As such, a pulse is generated every time magnetic flux is detected by the receiver. Since motor control circuits used for operators do not have automatic speed compensation, the speed is directly proportional to the load. Therefore, the heavier the load, the slower the rotation of the motor. The optical or magnetic encoder counts the number of pulses in a predetermined amount of time. If the motor slows down, the count is less than if the motor moved at its normal speed. Accordingly, the internal entrapment device triggers as soon as the number of pulses counted falls below a manually set threshold during the predetermined period of time.
While the optical encoder wheels or magnetic flux pick-up sensors may be employed with closed loop systems, this method of entrapment protection cannot accurately detect the down motion of an open loop system wherein the door is not directly attached to the operator. This condition is made worse by the use of very light doors which require very little counterbalance torsional force. If the door does not move at the beginning of the close cycle, when the weight of the door against the counterbalance systems is the lowest and the tension from the springs are the lowest, the motor can make several revolutions and the drums can peel off a considerable amount of cable before the torsional force of the springs, no longer counterbalanced by the weight of the door, induces enough force on the motor to slow the motor for the pulse counter system to detect and trigger the internal entrapment system.
From the foregoing discussion it will be appreciated that as a residential garage door travels in the opening and closing directions, the force needed to move the garage door varies depending upon the door position or how much of the door is in the vertical position. Counterbalance springs are designed to keep the door balanced at all times if the panels or sections of the door are uniform in size and weight. The speed of the door panels as they traverse the transition from horizontal to vertical and from vertical to horizontal can cause variations in the force requirement to move the door. Further, the panels or sections can vary in size and weight by using different height panels together or adding windows or reinforcing members to the panels or sections. In prior art devices, these variations cannot be compensated for. To compensate for these variations, a force setting must be set to overcome the highest force experienced to move the door throughout the distance the door travels. For example, the force to move door could be as low as 5 to 10 pounds at the first of the movement and increase to 35 to 40 pounds at another part of the movement. Therefore, the force setting on the operator must be least 41 pounds to assure the internal entrapment device will not activate. If an obstacle is encountered during the time the door is in the 35 to 40 pound region, it will take only 1 to 6 pounds of force against the object to activate the internal entrapment device. However, if the door is in the 5 to 10 pound region, the door will up to 31 to 36 pounds of force against the object before the internal entrapment device activates. To exacerbate this condition, the force adjustments on these internal entrapment devices can be adjusted by the consumer or the installer to allow the operator to exert several hundred pounds of force before the internal entrapment device will activate. As such, it is common to find garage door operators that can crush automobile hoods and buckle garage door panels before the internal entrapment system is triggered.
Two patents have attempted to address the shortcomings of properly triggering internal entrapment systems. One such patent, U.S. Pat. No. 5,278,480 teaches a microprocessor system which learns the open and closed position limits as well as force sensitivity limits for up and down operation of the door. This patent also discloses that the closed position limit and the sensitivity limits are adaptably adjusted to accommodate changes in conditions to the garage door. Further, this system may "map" motor speed and store this map after each successful closing operation. This map is then compared to the next closing operation so that any variations in the closing speed indicate that an obstruction is present. Although this patent is an improvement over the aforementioned entrapment systems, several drawbacks are apparent. First, the positional location of the door is provided by counting the rotations of the motor with an optical encoder. As discussed previously, optical encoders and magnetic flux pickup sensors are susceptible to interference and the like. This system also requires that a sensitivity setting must be adjusted according to the load applied. As noted previously, out of balance conditions may not be fully considered in systems with an encoder. Although each open/close cycle is updated with a sensitivity value, the sensitivity adjustment is set to the lowest motor speed recorded in the previous cycle. Nor does the disclosed system consider an out-of-balance condition or contemplate that different speeds may be encountered at different positional locations of the door during its travel.
Another patent, U.S. Pat. No. 5,218,282, also provides an obstruction detector for stopping the motor when the detected motor speed indicates a motor torque greater than the selected closing torque limit while closing the door. The disclosure also provides for at least stopping the motor when the detected motor speed indicates that motor torque is greater than the selected opening torque limit while opening the door. This disclosure relies on optical counters to detect door position and motor speed during operation of the door. As discussed previously, the positional location of the door cannot be reliably and accurately determined by pulse counter methods.